Along with developments of information communication technologies, requirements for information securities become stronger. Since an unpredictability in an information security technique depends on the quality of random numbers used, a performance of a random number generation circuit is very important. Roughly two different types of random number generation methods are available. A first method generates a pseudo random number sequence based on an algorithm, and a second method generates a random number sequence based on physical uncertain factors.
As a well-known method of generating random numbers using physical phenomena, a method of latching a fast oscillation signal by clocks sufficiently lower than that signal is available. When jitter is superposed on the fast oscillation signal, since a phase of the oscillation signal fluctuates with respect to clock timings, random outputs can be obtained. However, since the magnitude of the jitter is generally very smaller than an oscillation cycle, oscillation has to be repeated many times, thus posing a problem of an increase in consumption power accordingly. In order to reduce the consumption power, the number of oscillation times has to be reduced. For this purpose, the jitter has to have a larger magnitude with respect to the oscillation cycle, thereby improving the random number generation efficiency.